Association of State-Level Firearm-Related Deaths With Firearm Laws in Neighboring States.

Importance: Firearms are easily transported over state borders; hence permissive firearm laws in one state may have an interstate association with firearm-related deaths in nearby states. Objectives: To examine whether certain firearm laws have an interstate association with firearm-related deaths in nearby states. Design, Setting, and Participants: This cross-sectional observational study used data on state firearm-related deaths in the 48 contiguous states of the US between January 1, 2000, and December 31, 2019. A spatial autoregressive model with fixed effects for state and year was used to evaluate within-state, interstate, and overall associations between firearm laws and firearm-related deaths. Analyses were performed during January 2022. Exposures: The following 9 types of laws were evaluated: universal background checks for all firearms purchase, background checks for handgun sales at gun shows, license requirement to purchase all firearms, state dealer license requirement for handgun sales, requirement of retaining records of handgun sales, ban on purchasing a handgun on behalf of another, prohibition of firearm possession by persons who committed violent misdemeanors, required relinquishment of firearms for persons becoming prohibited from possessing them, and discretion in granting a concealed carry permit. Main Outcomes and Measures: State-level total firearm-related death rates, suicide rates, and homicide rates. Results: In sum, the study period included 662 883 firearm-related deaths of all intents. License requirement for firearm purchase had a within-state association (effect size, -1.79 [95% CI, -2.73 to -0.84]), interstate association (effect size, -10.60 [95% CI, -17.63 to -3.56]), and overall association (effect size, -12.38 [95% CI, -19.93 to -4.83]) per 100 000 population decrease in total firearm-related deaths. This law also had within-state association (effect size, -1.26 [95% CI, -1.72 to -0.80]), interstate association (effect size, -9.01 [95% CI, -15.00 to -3.02]), and overall association (effect size, -10.27 [95% CI, -16.53 to -4.01]) per 100 000 population decrease in firearm-related homicide. Conclusions and Relevance: The findings of this pooled cross-sectional analysis suggest that certain firearm laws in one state were associated with other states' firearm-related deaths. Synergic legislative action in adjacent states, federal firearm legislation, and measures that reduce migration of firearms across state borders should be part of the overarching strategy to prevent firearm-related deaths.